Method and apparatus for selectible quantization in an encoder

ABSTRACT

A method for selectable quantization for use in an encoder for compressing video and/or audio data includes processing that begins by receiving discrete cosine transform data of an encoded signal. The processing continues by obtaining a quantization table. The processing then continues by obtaining a plurality of scaling factors. The process then continues by generating a plurality of quantized value sets of the discrete cosine transform data based on the quantization table and the plurality of quantization scaling factors. The resulting data is then multiplied separately by each of the quantization scaling factors to produce the plurality of quantized values sets. The process then continues by selecting one of the plurality of quantized value sets based on quantization selection criteria.

TECHNICAL FIELD OF THE INVENTION

This invention relates generally to data compression processing and moreparticularly to quantization within such data compression processing.

BACKGROUND OF THE INVENTION

As is known, MPEG (motion picture expert group) audio and videocompression was developed for storing and distributing digital video andaudio signals. There are currently multiple versions of MPEG standardsincluding MPEG 1, MPEG 2, MPEG 4, and MPEG 7 with more versions likelyto come. The first of the MPEG standards, MPEG 1, was developed for usewith video compact disks (CDs), which have a bit rate of 1.416 megabitsper second, of which 1.15 megabits was for video. MPEG 2 was developedto cover a wider range of applications including high definitiontelevision, progressive scan videos, interlaced videos, DVDs, anddigital standard definition television. Such various digital formatshave bit rates ranging from 1.5 megabits per second to 60 megabits persecond. MPEG 4 uses an object-based approach where scenes are modeled ascompositions of objects, both natural and synthetic, with which the usermay interact. Visual objects in a scene are described mathematically andgiven a position in 2-dimensional or 3-dimensional space. Similarly,audio objects are placed in sound space. This enables the audio andvideo objects to be defined once and enables the viewer to change his orher viewing positions of the video and/or audio objects. MPEG 7standardizes the description of multimedia material such as stillpictures, audio and video regardless of whether the data is storedlocally, in remote databases or is broadcasted.

Regardless of the MPEG standard used, the basic architecture for an MPEGencoder and an MPEG decoder are similar. For example, an MPEG encoderincludes a motion compensation function, discrete cosine transform (DCT)function, quantization function, a zig-zag scan function, and anencoding function, such as run-length encoding or Huffman encoding. Themotion compensation function retrieves macro blocks of data from memoryfor a particular frame of video. As is known, a frame of MPEG video mayinclude an intra (I) frame, a predicted (P) frame, and/or abi-directional (B) frame. The motion compensation function utilizesmotion vectors, which specify where to retrieve a macro block of apreviously decoded frame, to remove temporal redundancies between B andP frames.

The discrete cosine transform function receives the compensated macroblock and performs a discrete cosine transform function thereon, wherethe discrete cosine transform function essentially filters the motioncompensated macro block of data utilizing a plurality of coefficientsorganized in a matrix. The result of the discrete cosine transformfunction is a discrete cosine transform matrix.

The quantization function receives the discrete cosine transform matrixand, utilizing a quantization matrix, or table, quantizes the DCT matrixto limit the number of allowed values for each coefficient. As is known,the quantization function is a primary source for loss in anycompression process.

The quantized data is then rendered in a zig-zag manner to produce alinear stream of data. The linear stream of data is then encoded using arun-length encoding, Huffman encoding et cetera process to produce theMPEG encoded data. An MPEG decoder includes similar componentsconfigured to perform the reverse function in the reverse order as theMPEG encoder.

Since the quantization function is a primary source for loss in MPEGencoding, a quantization table is selected to provide an accepted levelof loss (i.e., an accepted video quality) for worst case encodingconditions (e.g., fast moving action within a video). While this ensuresacceptable levels of video quality, it comes with the cost of processingmore data than is needed in most cases (i.e., when worst case encodingconditions are not encountered). This over processing is exasperatedwhen multiple video programs are being encoded. The same issue arisesfor all types of video and/or audio compression, including JPEG, MJPEG,et cetera.

Therefore, a need exists for a video and/or audio encoding method andapparatus that maintains a desired level of quality while reducingprocessing requirements.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a schematic block diagram of an encoder in accordancewith the present invention;

FIG. 2 illustrates a graphical representation of a quantization functionin accordance with the present invention;

FIG. 3 illustrates a graphical representation of a quantizer inaccordance with the present invention;

FIG. 4 illustrates a graphical representation of sectional quantizing inaccordance with the present invention;

FIG. 5 illustrates a logic diagram of a method for selectablequantization in accordance with the present invention;

FIG. 6 illustrates a logic diagram of an alternate method for selectablequantization in accordance with the present invention;

FIG. 7 illustrates a logic diagram of a further method for selectablequantization in accordance with the present invention;

FIG. 8 illustrates a logic diagram of a method for controlling theamount of quantization processing in accordance with the presentinvention;

FIGS. 9 and 10 illustrate further processing of the method of FIG. 8;

FIG. 11 illustrates a logic diagram of an alternate method forcontrolling the amount of quantization processing in accordance with thepresent invention; and

FIG. 12 illustrates a logic diagram of a further method for controllingthe amount of quantization processing in accordance with the presentinvention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Generally, the present invention provides a method for selectablequantization for use in an encoder for compressing video and/or audiodata. Such a method and apparatus includes processing that begins byreceiving discrete cosine transform data of an encoded signal. Theencoded signal may be an MPEG encoded signal, which includes MPEG 1,MPEG 2, MPEG 4 and/or MPEG 7 data, JPEG encoded, MJPEG, and/or signalcompressed using any other compression technique of audio and/or videodata. The processing continues by obtaining a quantization table. Forexample, the quantization table may be as defined in the IOS/IEC 14496-2specification for default matrixes for intrablocks and default matrixfor non-intrablocks (B frames and P frames). The processing thencontinues by obtaining a plurality of scaling factors. The process thencontinues by generating a plurality of quantized value sets of thediscrete cosine transform data based on the quantization table and theplurality of quantization scaling factors. For example, the discretecosine transform data is presented in an 8×8 matrix, which is multipliedby an 8×8 matrix constituting the quantization table. The resulting datais then multiplied separately by each of the quantization scalingfactors to produce the plurality of quantized values sets. The processthen continues by selecting one of the plurality of quantized value setsbased on quantization selection criteria. For example, the quantizationselection criteria may have a certain threshold for a number of zeros ina resulting set, where, the more zeros in the set, the less data thereis available to reconstruct the picture. Thus, for complex pictures,such as the video associated with a football game, requires more data toreconstruct than simple pictures, such as a picture of a blue sky.Accordingly, a certain number of zeros may be acceptable within theresulting quantized data without degradation of the video image. Withsuch a method and apparatus, the level of quantization may be variedfrom frame to frame to optimize the number of bits processed to produceencoded data while maintaining video quality.

The present invention can be more fully described with reference toFIGS. 1 through 12. FIG. 1 illustrates a schematic block diagram of anencoder 10. Such an encoder 10 may be utilized to encode video and/oraudio data in accordance with one of the MPEG standards, JPEG standard,MJPEG standard, and/or any other technique used to compress video and/oraudio data. The encoder 10 includes a motion estimation module 12, adiscrete cosine transform (DCT) module 14, a quantizer 16, a zig-zagmodule 18, a Huffman encoder 20 (or run-length encoder, or any othertype of encoder), an output bit bucket 22, memory controller 32, memory30, motion compensation module 24, an inverse discrete cosine transformmodule (IDCT) 26 and a decoder instruction packet module 28. The motionestimation module 12, the DCT module 14, the quantizer 16, the zig-zagmodule 18 and/or the Huffman encoder 20 may be implemented utilizingprocessing module 34. The processing module 34 may be a singleprocessing device or a plurality of processing devices. Such aprocessing device may be a microprocessor, microcontroller,microcomputer, digital signal processor, central processing unit,programmable logic array, programmable logic device, state machine,logic circuitry, and/or any device that manipulates signals (analogand/or digital) based on operational instructions. The operationalinstructions may be stored in memory 30. Memory 30 may be a singlememory device or a plurality of memory devices. Such a memory device maybe non-volatile memory, volatile memory, static memory, dynamic memory,random access memory, read-only memory, magnetic tape memory, and/or anydevice that stores digital information.

In operation, the motion estimation module 12 is operably coupled toreceive raw frame unit data 38 in macro blocks, motion vectors 36 and toretrieve data for predicted frames and/or bi-directional frames frommemory 30 via memory controller 32. In general, the motion compensationfunction improves compression of P and B frames by removing temporalredundancies between the frames. Such motion compensation relies on thefact that within a short sequence of the same general image, mostobjects remain in the same location while other objects move only ashort distance. The motion is described as a 2-dimensional motion vectorthat specifies where to retrieve a macro block from a previously decodedframe to predict the sample values of the current macro block. After amacro block has been compressed using motion compensation, it containsboth the spatial difference (motion vectors) and content difference(error terms) between the reference macro block and the macro blockbeing coded. Macro blocks in B frames are coded using either the closestprevious or future I or P frames as a reference resulting in fourpossible codings: (1) Intracoding, where no motion compensation isutilized, (2) forward prediction, where the closest previous I or Pframe is used as a reference, (3) backward prediction, where the closestfuture I or P frame is used as a reference, or (4) bi-directionalprediction where two frames are used as a reference, either the closestprevious I frame or P frame and the closest future I or P frame.

The discrete cosine transform (DCT) module 14 receives the motionestimation data and performs a discrete cosine transform functionthereon. Typically, the discrete cosine transform function operates onan 8×8 block of input samples or prediction error terms, which areprocessed utilizing an 8×8 DCT resulting in an 8×8 block of horizontaland vertical frequency coefficients. The result is the discrete cosinetransform data, which is an 8×8 matrix block.

The quantizer 16 receives the discrete cosine transform data andquantizes the data in accordance with the concepts further describedwith reference to FIGS. 2 through 12. In general, the quantizer 16 willquantize the DCT data in a manner, which reduces the processing steps ofthe overall encoding while maintaining an acceptable level of videoand/or audio quality when the compressed data is decompressed.

The zig-zag module 18 receives the quantized data and converts thequantized data, which is a matrix, for example an 8×8 block into alinear stream of quantized frequency coefficients that are arranged inan order of increasing frequency. As such, a long run of zerocoefficients is produced.

The Huffman encoder 20 receives the linear stream of quantized frequencycoefficients and encodes them to produce the encoded data. Thefunctionality of a Huffman encoder, or run-length encoder is known, thusno further discussion will be presented except to further illustrate theconcepts of the present invention.

The output bit bucket 20 receives the encoded data from the Huffmanencoder as a serial bit stream. The output bit bucket 22 converts theserial bit stream of the encoded data into bytes of data or data wordsthat are formatted in accordance with the size of memory 30. Forinstance, if a data word in memory is 1 byte, the output of the outputbit bucket 22 is 1 byte. As a further example, if the memory has amemory of 32 bits or 4 bytes, the output of the output bit bucket 22 is32 bits or 4 bytes.

The motion compensation module 24 and the IDCT module 26 are utilized toself-check the encoding process. In addition, the modules are utilizedto establish a desired level of video quality. For example, thequantizer 16, as will be described in greater detail with reference toFIGS. 2 through 12, can vary the level of quantization to reduce thenumber of bits processed to encode the frame of data. By performing aninverse discrete cosine transform function and the motion compensation,the quantized data is converted back into the raw data. By comparing therestructured raw data with the original raw data, a determination may bereadily made as to whether the level of quantization is at a sufficientlevel to ensure video quality. For example, if the recaptured frame datais substantially similar to the raw data, the quantization levelutilized by quantizer 16 may be too high. As such, a greater level ofquantization may be utilized. When the recaptured frame data differs infrequencies of significance from the raw data, the level of quantizationis too great, thus it needs to be reduced. As such, the encoder mayinclude a self-checking mechanism to ensure that the encoder isprocessing the least amount of bits necessary to achieve a desired levelof video and/or audio quality when recapturing the compressed data. Inaddition, the raw data is written back into memory for subsequent use asa reference frame.

FIG. 2 illustrates a graphical representation of the quantizationprocess utilized by quantizer 16. As shown, the DCT data 42 is an 8×8matrix where the subscript i corresponds to the column number and thesubscript j corresponds to the row number. The quantization table 44(Q(i,j)) is an 8×8 matrix where i corresponds to the column number and jcorresponds to the row number. As is known, the most relevant data inthe DCT data 42 originates in the upper left (i.e., zero, zero) positionand decreases as the row and column number increase. As such, verysimple frames of data (such as a picture of a blue sky) have data ofsignificance only in a few positions within the matrix of the DCT data42. As the complexity of the picture increases, frames of the picturewill have data of significance in more and more of the matrix positionsof the DCT data 42. As graphically illustrated, as the complexity of thepicture increases, the complexity levels 52 of the matrix increases.

For simple pictures, ones having minimal complexity levels 52 of thematrix, there will be a substantial number of insubstantial data values54. As the complexity level 52 of the matrix increases the number ofinsubstantial data values will decrease.

The quantization table 44 includes a plurality of values, which are usedto divide the DCT data 42. An I frame will have a different defaultmatrix than a B or P frame. The values in the quantization tableincrease in value as the row and column numbers increase. Accordingly,as the DCT data 42 is divided by the quantization table 44, the smallerdata values of the DCT data are being divided by larger values than thelarger data values, which produces the insubstantial data values 54. Theresulting matrix will have a similar pattern of complexity levels ofinsubstantial data values as the DCT data 42. The resulting matrix isthen multiplied by the scaling factor 46 (Qs). The scaling factorfurther reduces the values in the resulting matrix thus producing thequantization value set 40 (T(I_(i,j))).

By utilizing a plurality of scaling factors 46, a plurality ofquantization value sets is obtained. This may be further illustratedwith reference to FIG. 3.

FIG. 3 illustrates quantizer 16 that includes a plurality of scalingfactors (Q1–QN) 60–64, a plurality of insubstantial determinationmodules 66–70, and a selection module 72. Each of the scaling factormodules 60–64 is operably coupled to receive respective quantizationmatrix 75, which is the product of the DCT data divided by thequantization table 74. Each of the scaling factors 60–64 scales theresultant matrix 75 by the corresponding scaling factor (Q1–Qn). Theoutput of each scaling factor module 60–64 is a quantized value set.

Each of the insubstantial data determination modules 66–70 receives acorresponding one of the quantized value sets from an associated scalingfactor module 60–64. The insubstantial data determination module 66–70,for its respective quantized value set, determines a boundary of theresultant matrix data, which delineates data of significance from theinsubstantial data. Such a determination corresponds with the level ofcomplexity and insubstantial data as illustrated in FIG. 2. For example,the output of each insubstantial data determination module 66–70 mayinclude a list of matrix positions by column and row of significant dataand/or of insubstantial data. Alternatively, the output may indicatejust a number of matrix positions that include substantial data and/orinsubstantial data. Note that a data value in the resulting matrix isdetermined to be insubstantial if it is insignificant with respect tothe data value in the (0,0) position of the matrix. Generally, data willbe insignificant if it is 1/20^(th) to 1/1000^(th) of the (0,0) value.As is known, the (0,0) value corresponds to the DC component of thedata.

The selection module 72 is operably coupled to each of the insubstantialdata determination modules 66–70. The selection module 72, based ondecision inputs 76, selects one of the quantized value sets from thescaling factor modules 60–64 as the selected quantized value set 78. Thedecision inputs 76 may be based on the complexity of the matrix of datavalues in the DCT data 42 where the greater complexity of the matrixresults in a lower level of desired quantization and the lessorcomplexity of the matrix results in a higher level of desiredquantization. Alternatively, the decision input 76 may be based on adesired number of insubstantial data values. Such a number ofinsubstantial data values corresponds to the level of complexity of thematrix. In addition, the decision input 76 may correspond to a desiredlevel of video quality. As is known, as the level of quantizationincreases, the ability to recapture the raw data decreases thusdecreasing the video quality. As such, the video quality threshold maybe established to determine the level of insubstantial data that isallowable.

As an example of the operation of quantizer 16 of FIG. 3, assume thatfor a given picture the threshold for the number of insubstantial datavalues has been set to be 24, which means that 40 of the 64 positions inthe matrix of the DCT data includes data of significance. Furtherassume, that the scaling factor Q1 is larger than scaling factor Q2which is larger than scaling factor Q3, et cetera. As such, the outputof scaling factor module 60 should have fewer resulting insubstantialvalues than the output of scaling factor 64.

The insubstantial data determination modules 66–70 receive therespective quantization matrix 75 and determine the number ofinsubstantial data values. For this example, assume that theinsubstantial data determination module 66 determine that thequantization matrix 75 from scaling factor 60 has 22 insubstantial datavalues, while insubstantial data determination module 60 determines thatthe quantization matrix 75 from scaling factor module 62 has 23insubstantial data values and further assume that the insubstantial datadetermination module 70 determines that the output of scaling factormodule 64 has 24 insubstantial values. The selection module receives theindication of insubstantial data values in each of the correspondingmatrixes. Based on the inputs that indicate that 24 insubstantial datavalues in the matrix is acceptable, selection module 72 would select thequantization matrix 75 from the scaling factor module 64. As such, byprocessing less of the matrix, less data is being processed by theencoder, thereby improving throughput and/or processing resources whilemaintaining a desired level of video quality.

In addition to the various scaling factors utilized in FIG. 3 or as analternative to the various scaling factors, a picture may be partitionedinto regions as illustrated in FIG. 4. Each region is assigned acorresponding number of bits to quantize the data. If the number of bitsfor a preceding region is exceeded in quantizing the data, the scalingfactor used to quantize the next region is reduced. From region toregion, the cumulative bits used to quantize the data are maintainedsuch that the overall encoded picture 80 is encoded utilizingapproximately a desired number of bits.

As shown, the encoded picture includes a plurality of macro blocks. AnMPEG encoded picture 80 includes 16×16 macro blocks. Each macro block 82includes 16 samples×16 lines. The macro block 82 may be further dividedinto 4 blocks 84 that each includes 8 samples×8 lines. As such, theregional partitioning of the quantization of an encoded picture 80 maybe done in regions as shown by regions 1–4, at the macro block level 82,and/or at the block level 84.

FIG. 5 illustrates a logic diagram of a method for selectablequantization. The process begins at Step 90 where discrete cosinetransform data of an encoded signal is received. The discrete cosinetransform data may be produced by performing a discrete cosine transformfunction upon a macro block of MPEG encoded data, wherein the discretecosine transform data includes a matrix of data values. The process thenproceeds to Step 92 where a quantization table is obtained. One type ofquantization table was illustrated and discussed with reference to FIG.2. The process then proceeds to Step 94 where a plurality ofquantization scaling factors is obtained.

The process then proceeds to Step 96 where a plurality of quantizedvalue sets are generated from the discrete cosine transform data basedon the quantization table and the plurality of quantization scalingfactors. This may be done by performing the equationt(i,j)=D(i,j)/[Q(i,j)*Qs], where i represents a row number of thematrix, j represents a column number of the matrix, t(i,j) represents aquantized value set of the plurality of quantized value sets, D(i,j)represents the matrix of discrete cosine transform data, Q(i,j)represents the quantization table, and Qs represents one of theplurality of quantization scaling factors.

The process then proceeds to Step 98 where one of the plurality ofquantized value sets is selected based on quantization selectioncriteria. The quantization selection criteria may include the complexityof the matrix of data values wherein the greater the complexity of thematrix of data values results in a lower level of desired quantizationand the lessor complexity of the matrix of data values results in ahigher level of desired quantization.

As an alternative method for selecting one of the quantized value sets,the process may proceed to Steps 100–108. At Step 100, a determinationis made for each of the plurality of quantized value sets to determinethe number of insubstantial data values in the quantized value set.Insubstantial data values correspond to values within the matrix withrespect to the DC value within the matrix. As is known, the DC valuewithin the matrix corresponds to position zero, zero while AC componentsof the matrix correspond to the other positions in the matrix.Accordingly, when the data value is 1/20^(th) to 1/1000ths or less thanthe DC component, the data may be determined to be insubstantial.

The process then proceeds to Step 102 where a determination is made asto an acceptable level of insubstantial data values. This may be done asshown in Steps 106 and 108. At Step 106, a video quality threshold isestablished. This is based on a desired level of resolution of thepicture and may further be based on the type of picture. For example, ifthe picture includes a lot of motion and contrasting images, thethreshold for insubstantial values would be lower, (i.e., wanting moredata to be processed) than if the images contain little motion andlittle contrast. The process then proceeds to Step 108 where theacceptable level of insubstantial data values is determined based on thevideo quality threshold.

The process then returns to Step 104 where one of the plurality ofquantized value sets is selected based on the acceptable level ofinsubstantial data values and the number of insubstantial data values.

FIG. 6 illustrates a logic diagram of an alternate method for selectablequantization. The process begins at Step 110 where a plurality ofquantization matrixes is generated from discrete cosine transform databased on a quantization table and a plurality of quantization scalingfactors. This may be done by performing the following equationt(i,j)=D(i,j)/[Q(i,j)*Qs], where i represents a row number of thematrix, j represents a column number of the matrix, t(i,j) represents aquantized value set of the plurality of quantized value sets, D(i,j)represents the matrix of discrete cosine transform data, Q(i,j)represents the quantization table, and Qs represents one of theplurality of quantization scaling factors. The discrete cosine transformdata may be derived by performing a discrete cosine transform functionupon a macro block of MPEG encoded data, where the discrete cosinetransform data includes a matrix of data values.

The process then proceeds to Step 112 where the plurality ofquantization matrixes is analyzed to identify one of the plurality ofquantization matrixes having a best-match of reduced data content andacceptable video quality. This may be done by determining a number ofinsubstantial data values within each of the quantization matrixes.Having done this, a determination would then be made as to an acceptablelevel of insubstantial data values. Then, the best-match will beestablished based on the quantization matrix having substantially thesame number of insubstantial data values as indicated by the acceptablelevel of insubstantial data values. For example, if the image beingdisplayed is a blue sky, the number of insubstantial data values may bein the neighborhood of 60. Thus, if one quantization matrix has 55insubstantial data values, another has 57, another has 60, the onehaving the 60 insubstantial data values would be utilized. This reducesthe number of bits that needs to be processed to encode the video imageswhile maintaining the desired level of video quality.

The process then proceeds to Step 114 where one of the plurality ofquantized matrixes is selected for processing.

FIG. 7 illustrates a logic diagram of a method for encoding data. Theprocess begins at Step 120 where motion estimation is performed upon ablock of data (which may be a macro block of MPEG encoded data) based onmotion vectors. Such motion estimation was described with reference toFIG. 1. The process then proceeds to Step 122 where a discrete cosinetransform function is performed upon the motion estimated data. Theprocess then proceeds to Step 124 where a plurality of quantizationmatrixes of the discrete cosine transform data is generated based on aquantization table and a plurality of quantization scaling factors. Thisis a similar step as Step 96 of FIG. 5.

The process then proceeds to Step 126 where one of the plurality ofquantization matrixes is selected based on a best-match of reduced datacontent and acceptable video quality. The process then proceeds to Step128 where a zig-zag function is performed upon the quantized data. Theprocess then proceeds to Step 130 where a run-level, or Huffman encodingis performed upon the zig-zag data to produce the resulting encodeddata.

FIG. 8 illustrates a logic diagram of a method for controlling an amountof quantization processing. The process begins at Step 140 wherediscrete cosine transform data of a block of a frame of data isreceived. For example, the block of data may correspond to a macro blockof an MPEG encoded video and/or audio frame. The process then proceedsto Step 142 where a quantization table is obtained for the particularframe of data. For example, if the frame of data being processed is an Iframe of MPEG data, one type of quantization table will be retrieved. Ifthe frame of data corresponds to a B or P frame, another quantizationtable would be retrieved.

The process then proceeds to Step 144 where a quantization scalingfactor related to the frame is obtained. The quantization scaling factormay be determined by the desired level of video quality and/or anacceptable level of insubstantial data values. The process then proceedsto Step 146 where a determination is made as to whether quantizationprocessing limits have been exceeded for quantization of precedingblocks of the frame of data. In general, the quantization of a frame ofdata has a predetermined level of processing resources to perform such afunction. To ensure that the processing maintains within those limits,the frame of data is divided into regions. The regions may vary frombisecting the frame into two sections down to the block level asillustrated in FIG. 4.

One technique for determining whether the quantization processing limitshave been exceeded is illustrated via Steps 156–166. At Step 156, aregion of the frame in which the block that is currently being processedis determined. The processing then proceeds to Step 158 where adetermination is made as to the number of bits used to quantize apreceding region of the frame that includes the previously processedblocks. The process then proceeds to Step 160 where a determination ismade as to whether the number of bits used to process the precedingblocks exceeds a bit threshold for the region. The bit thresholdcorresponds to a linear allocation of the total number of bits availablefor processing a frame or some other desired function. At Step 162, adetermination is made as to whether the threshold was exceeded. If not,the process proceeds to Step 164 where no indication that the processinglimits have been exceeded is given. If, however, the threshold wasexceeded, the process proceeds to Step 166 where an indication that thequantization processing limits have been exceeded is provided.

Returning to the main flow, at Step 148, the process branches based onwhether the quantization processing limits have been exceeded. If not,the process proceeds to Step 150 where quantization data is generatedbased on the discrete cosine transform data, the quantization table andthe quantization scaling factor.

If, however, the processing limits have been exceeded, the processproceeds to Step 152 where the quantization scaling factor is increased.By increasing the scaling factor, the level of quantization isincreased, thus reducing the number of bits that needs to be processedto quantize the data results. The process then proceeds to Step 154where quantization data is generated based on the discrete cosinetransform data, the quantization table, and the increase quantizationscaling factor.

FIG. 9 illustrates a logic diagram that further describes thedetermination of whether the quantization processing limits have beenexceeded as indicated in Step 146 of FIG. 8. The process begins at Step170 where an assigned total number of processing bits are quantizing theframe is obtained. Such a number will be based on the type of signalbeing encoded, the processing capabilities of the encoder and the numberof other functions being supported by the processor. The process thenproceeds to Step 172 where a determination is made as to the number ofbits per block of the frame, which is based on a number of blocks in theframe and the assigned total number of processing bits. For example, if1,000,000 bits are allocated for processing the frame and the frame isdivided into 4 blocks, each block, or region, may have 250,000 bits forprocessing the block.

The process then proceeds to Step 174 where the number of bits used toquantize the data of each of the previously processed blocks in theframe is recorded. The process then proceeds to Step 176 where thenumber of bits used to quantize data of each of the previous processedblocks is summed to produce a current number of bits used. The processthen proceeds to Step 178 where a current ideal number of bits iscalculated based on the number of bits per block and a number of blocksof the previously processed blocks. For instance, utilizing the previousexample of 1,000,000 bits for the entire frame where each block has250,000 bits for processing the quantization, and further assuming thatthe 3^(rd) block is being processed, the current ideal number of bitswould be 500,000, which corresponds to the 1^(st) 2 blocks each having250,000 bits.

The process then proceeds to Step 180 where, when the current number ofbits used exceeds the current ideal number of bits, indicating that thequantization processing limits have been exceeded. Continuing with theprevious example, if the 1^(st) block required 245,000 bits to processand the 2^(nd) block required 270,000 bits, the cumulative bit number is515,000 bits, which exceeds the current ideal number. Accordingly, thequantization scaling factor for block 3 would be increased such that thenumber of bits to quantize this particular block would be decreased.

FIG. 10 illustrates further processing to increase the quantizationscaling factor of Step 152 of FIG. 8. Such processing begins at Step 182where an amount in which the quantization processing limits have beenexceeded is determined. The process then proceeds to Step 184 where adetermination is made as to whether the excess amount exceeds athreshold. At Step 186, the process branches based on whether thethreshold has been exceeded. If not, the process proceeds to Step 188where the increase quantized scaling factor is used. If, however, thethreshold is exceeded, the process proceeds to Step 190 where a 2^(nd)increase quantization scaling factor is used, which further increasesthe quantization of the data with respect to the increase quantizationscaling factor. In essence, what is being taught with respect to FIG. 10is that if the number of bits used to process preceding blocks slightlyor moderately exceeds the bit quantity, the scaling factor isincremented to the desired next level. If, however, the processing of apreceding block substantially exceeds the allocated bit processing levelfor the scaling factor may be further increased in multiple incrementsas opposed to a single increment.

FIG. 11 illustrates a logic diagram of an alternate method forcontrolling the amount of quantization processing. The process begins atStep 200 where a frame of MPEG encoded data is partitioned into aplurality of regions. This may be done by partitioning the MPEG encodeddata on a macro block basis such that each macro block is an uniqueregion, at the block level such that each block is an individual regionor the MPEG encoded data may be divided into a number of regions whereeach region includes multiple macro blocks. Such a division wasillustrated graphically with reference to FIG. 4.

The process then proceeds to Step 202 where a desired bit processingvalue is assigned to each of the plurality of regions. This may be doneby dividing a total number of desired bits for quantizing the frame ofdata by the number of regions thus producing a linear allocation of bitprocessing.

The process then proceeds to Step 204 where quantization of at least oneblock of the frame of MPEG encoded data is monitored to obtain thenumber of bits used to quantize the block of data. The process thenproceeds to Step 206 where, when the bits used to quantize the block fora region of the frame exceeds the desired bit processing value for theregion, the quantization scaling factor for quantizing the data isincreased. The increasing of the quantization scaling factor may be doneas described with reference to FIG. 10.

FIG. 12 illustrates a logic diagram of a method for encoding data. Theprocess begins at Step 210 where motion estimation is performed upon ablock of data based on motion vectors. For example, if the datacorresponds to MPEG data, the motion estimation performed was describedwith reference to FIG. 1. The process then proceeds to Step 212 where adiscrete cosine transform function is performed upon the motionestimated data. The process then proceeds to Step 214 where aquantization table is obtained. The process then proceeds to Step 216where a quantization scaling factor is obtained. The process thenproceeds to Step 216 where a determination is made as to whetherquantization processing limits have been exceeded for quantization ofpreceding blocks of data. Such a determination has been described withreference to FIGS. 8 through 11.

The process then proceeds to Step 218 where the process branches basedon whether the quantization processing limits have been exceeded. If so,the process proceeds to Step 220 where the quantization scaling factoris increased to produce an increased quantization scaling factor. Theprocess then proceeds to Step 222 where quantization data is generatedbased on the discrete cosine transform data, the quantization table andthe increased quantization scaling factor.

If the quantization processing limits have not been exceeded, theprocess proceeds to Step 228. At Step 228, quantization data isgenerated based on the discrete cosine transform data, the quantizationtable and the initial scaling factor. The process then proceeds fromStep 228 or Step 222 to Step 224. At Step 224, a zig-zag function isperformed upon the quantized data. The process then proceeds to Step 226where a run-level encoding and/or Huffman encoding is performed upon thezig-zag data to produce the desired encoding data.

The preceding discussion has presented a method and apparatus forreducing processing requirements within a video compression system whilemaintaining video quality for the recapturing of the video data. As oneof average skill in the art will appreciate, other embodiments may bederived from the teaching of the present invention without deviatingfrom the scope of the claims.

1. A method for selectable quantization, the method comprises:performing a discrete cosine transform function upon a macroblock ofMotion Picture Expert Group (MPEG) encoded data of an encoded signal toproduce discrete cosine transform data, wherein the discrete cosinetransform data includes a matrix of data values; receiving discrete thecosine transform data of the encoded signal; obtaining a quantizationtable; obtaining a plurality of quantization scaling factors; generatinga plurality of quantized value sets of the discrete cosine transformdata based on the quantization table and plurality of quantizationscaling factors; determining quantization selection criteria based oncomplexity of the matrix of data values, wherein greater complexity ofthe matrix of data values results in a lower level of desiredquantization and wherein lesser complexity of the matrix of data valuesresults in a higher level of desire quantization; and selecting one ofthe plurality of quantized value sets based on the quantizationselection criteria to produce quantized data.
 2. The method of claim 1,wherein the generating the plurality of quantization value sets furthercomprises: performing t(i,j)=D(i,j)/[Q(i,j)]*Qs, where i represents arow number of the matrix, j represents a column number of the matrix,t(i,j) represents a quantized value set of the plurality of quantizedvalue sets, D(i,j) represents the matrix of discrete cosine transformdata, Q(i,j) represents the quantization table, and Qs represents one ofthe plurality of quantization scaling factors.
 3. The method of claim 1,wherein the selecting the one of the plurality of quantized value setsfurther comprises: for each of the plurality of quantized value sets,determining number of insubstantial data values in the quantized valueset; determining an acceptable level of insubstantial data values; andselecting the one of the plurality of quantized value sets based on theacceptable level of insubstantial data values and the number ofinsubstantial data values in each of the plurality of quantized valuesets.
 4. The method of claim 3, wherein the determining an acceptablelevel of insubstantial data values further comprises: establishing avideo quality threshold; and determining the acceptable level ofinsubstantial data values based on the video quality threshold.
 5. Anapparatus for selectable quantization, the apparatus comprises:processing module; and memory operably coupled to the processing module,wherein the memory includes operational instructions that cause theprocessing module to: perform a discrete cosine transform function upona macroblock of Motion Picture Expert Group (MPEG) encoded data of anencoded signal to produce the discrete cosine transform data, whereinthe discrete cosine transform data includes a matrix of data valuesreceive the discrete cosine transform data of the encoded signal; obtaina quantization table; obtain a plurality of quantization scalingfactors; generate a plurality of quantized value sets of the discretecosine transform based on the quantization table and plurality ofquantization scaling factors; determining quantization selectioncriteria based on complexity of the matrix of data values, whereingreater complexity of the matrix of data values results in a lower levelof desired quantization and wherein lesser complexity of the matrix ofdata values results in a higher level of desire quantization; and selectone of the plurality of quantized value sets based on the quantizationselection criteria to produce quantized data.
 6. The apparatus of claim5, wherein the memory further comprises operational instructions thatcause the processing module to generate the plurality of quantizationvalue sets by: performing t(i,j)=D(i,j)/[Q(i,j)]*Qs, where i representsa row number of a matrix, j represents a column number of a matrix,t(i,j) represents a quantized value set of the plurality of quantizedvalue sets, D(i,j) represents the matrix of discrete cosine transformdata, Q(i,j) represents the quantization table, and Qs represents one ofthe plurality of quantization scaling factors.
 7. The apparatus of claim5, wherein the memory further comprises operational instructions thatcause the processing module to select the one of the plurality ofquantized value sets by: for each of the plurality of quantized valuesets, determining number of insubstantial data values in the quantizedvalue set; determining an acceptable level of insubstantial data values;and selecting the one of the plurality of quantized value sets based onthe acceptable level of insubstantial data values and the number ofinsubstantial data values in each of the plurality of quantized valuesets.
 8. The apparatus of claim 7, wherein the memory further comprisesoperational instructions that cause the processing module to determinean acceptable level of insubstantial data values by: establishing avideo quality threshold; and determining the acceptable level ofinsubstantial data values based on the video quality threshold.
 9. Amethod for selectable quantization, the method comprises: receivingdiscrete cosine transform data of an encoded signal; obtaining aquantization table; obtaining a plurality of quantization scalingfactors; generating a plurality of quantized value sets of the discretecosine transform data based on the quantization table and plurality ofquantization scaling factors; and selecting one of the plurality ofquantized value sets based on quantization selection criteria to producequantized data by: determining number of insubstantial data values inthe quantized value set, for each of the plurality of quantized valuesets; determining an acceptable level of insubstantial data values; andselecting the one of the plurality of quantized value sets based on theacceptable level of insubstantial data values and the number ofinsubstantial data values in each of the plurality of quantized valuesets.
 10. The method of claim 9, wherein the receiving the discretecosine transform data further comprises: performing a discrete cosinetransform function upon a macroblock of Motion Picture Expert Group(MPEG) encoded data to produce the discrete cosine transform data,wherein the discrete cosine transform data includes a matrix of datavalues.
 11. The method of claim 10, wherein the generating the pluralityof quantization value sets further comprises: performingt(i,j)=D(i,j)/[Q(i,j)]*Qs, where i represents a row number of thematrix, j represents a column number of the matrix, t(i,j) represents aquantized value set of the plurality of quantized value sets, D(i,j)represents the matrix of discrete cosine transform data, Q(i,j)represents the quantization table, and Qs represents one of theplurality of quantization scaling factors.
 12. The method of claim 9,wherein the determining an acceptable level of insubstantial data valuesfurther comprises: establishing a video quality threshold; anddetermining the acceptable level of insubstantial data values based onthe video quality threshold.
 13. An apparatus for selectablequantization, the apparatus comprises: processing module; and memoryoperably coupled to the processing module, wherein the memory includesoperational instructions that cause the processing module to: receivediscrete cosine transform data of an encoded signal; obtain aquantization table; obtain a plurality of quantization scaling factors;generate a plurality of quantized value sets of the discrete cosinetransform based on the quantization table and plurality of quantizationscaling factors; and select one of the plurality of quantized value setsbased on quantization selection criteria to produce quantized data by:determining number of insubstantial data values in the quantized valueset, for each of the plurality of quantized value sets; determining anacceptable level of insubstantial data values; and selecting the one ofthe plurality of quantized value sets based on the acceptable level ofinsubstantial data values and the number of insubstantial data values ineach of the plurality of quantized value sets.
 14. The apparatus ofclaim 13, wherein the memory further comprises operational instructionsthat cause the processing module to receive the discrete cosinetransform data by: performing a discrete cosine transform function upona macroblock of Motion Picture Expert Group (MPEG) encoded data toproduce the discrete cosine transform data, wherein the discrete cosinetransform data includes a matrix of data values.
 15. The apparatus ofclaim 14, wherein the memory further comprises operational instructionsthat cause the processing module to generate the plurality ofquantization value sets by: performing t(i,j)=D(i,j)/[Q(i,j)]*Qs, wherei represents a row number of a matrix, j represents a column number of amatrix, t(i,j) represents a quantized value set of the plurality ofquantized value sets, D(i,j) represents the matrix of discrete cosinetransform data, Q(i,j) represents the quantization table, and Qsrepresents one of the plurality of quantization scaling factors.
 16. Theapparatus of claim 13, wherein the memory further comprises operationalinstructions that cause the processing module to determine an acceptablelevel of insubstantial data values by: establishing a video qualitythreshold; and determining the acceptable level of insubstantial datavalues based on the video quality threshold.